amount button buy click code codes coupon customer discount friend help input item laid next paypal products sales tested trick

I set up coupon codes for each of my products as laid out in the Help section (go to each item, click next, put in the name/amount) but where does the customer input that code to get the discount? I use the Buy Now button and PayPal for my sales.

A friend tested it for me and said the code didn't work in PayPal.

Is there a trick to this?